Hi there! Today, we’re going to talk about one of the most important tools in programming: the for loop. This loop allows you to repeat actions multiple times, saving time and making your code cleaner and easier to understand.

What is a for loop?

A for loop is used when you need to repeat the same action multiple times. For example, if you want to print numbers from 1 to 10, instead of writing 10 separate lines of code, you can accomplish this with a for loop.

Syntax of the for Loop

The for loop has the following structure:

for (initialization; condition; update) {
    // code to be executed
}

Let’s break it down:

1. Initialization: This is where you create a variable, usually called a counter. For example, int i = 0;.
2. Condition: This checks whether the loop should continue running. As long as the condition is true, the loop will keep running.
3. Update: This changes the counter variable, typically by increasing it (e.g., i++).

Example 1: Printing Numbers from 1 to 5

Let’s write a program that prints numbers from 1 to 5:

public class Main {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            System.out.println("Number: " + i);
        }
    }
}

What’s happening here:

1. Initialization: int i = 1; — the loop starts with the variable i set to 1.
2. Condition: i <= 5; — the loop continues as long as i is less than or equal to 5.
3. Update: i++ — after each iteration, i is increased by 1. The loop stops when i exceeds 5.

Example 2: Multiplication Table for 3

Now, let’s create a program that prints the multiplication table for 3:

public class Main {
    public static void main(String[] args) {
        for (int i = 1; i <= 10; i++) {
            System.out.println("3 x " + i + " = " + (3 * i));
        }
    }
}

Output:

3 x 1 = 3
3 x 2 = 6
3 x 3 = 9
...
3 x 10 = 30

Here, the variable i starts at 1 and goes up to 10. During each iteration, the program multiplies 3 by i and prints the result.

Nested Loops

You can also have loops inside other loops. Let’s create a multiplication table for numbers 1 to 3:

public class Main {
    public static void main(String[] args) {
        for (int i = 1; i <= 3; i++) { // Outer loop
            for (int j = 1; j <= 10; j++) { // Inner loop
                System.out.println(i + " x " + j + " = " + (i * j));
            }
            System.out.println(); // Adds a blank line between tables
        }
    }
}

Example 3: Working with Arrays

The for loop is great for working with arrays. Here’s an example:

public class Main {
    public static void main(String[] args) {
        int[] numbers = {10, 20, 30, 40, 50};
        
        for (int i = 0; i < numbers.length; i++) {
            System.out.println("Array element: " + numbers[i]);
        }
    }
}

Here, the loop runs through each element of the array and prints it.

The for-each Loop

Java also has a simpler loop for working with arrays and collections, called the for-each loop:

public class Main {
    public static void main(String[] args) {
        int[] numbers = {10, 20, 30, 40, 50};
        
        for (int num : numbers) {
            System.out.println("Array element: " + num);
        }
    }
}

What’s happening here:

• int num is a temporary variable.
• : numbers tells the loop to go through every element in the numbers array.
• Each array element is assigned to num in turn, and we print it.

When to Use a for Loop?

Use a for loop when:

1. You know the exact number of times you need to repeat something (e.g., printing numbers from 1 to 10).
2. You’re working with arrays or lists.
3. You want to optimize your code and avoid writing the same action multiple times.

Homework

Try writing programs that:

1. Print all even numbers from 1 to 20.
2. Calculate the sum of numbers from 1 to 100.

Summing It Up

The for loop is a powerful tool for automating repetitive tasks. It makes your code more readable, efficient, and easy to modify. Once you master the for loop, you’ll be able to tackle a wide range of programming challenges with ease!